1-Wire Bus

Overview

1-Wire is a low speed half-duplex serial bus using only a single wire plus ground for both data transmission and device power supply. Similarly to I2C, 1-Wire uses a bidirectional open-collector data line, and is a single master multidrop bus. This means one master initiates all data exchanges with the slave devices. The 1-Wire bus supports longer bus lines than I2C, while it reaches speeds of up to 15.4 kbps in standard mode and up to 125 kbps in overdrive mode. Reliable communication in standard speed configuration is possible with 10 nodes over a bus length of 100 meters. Using overdrive speed, 3 nodes on a bus of 10 meters length are expected to work solid. Optimized timing parameters and fewer nodes on the bus may allow to reach larger bus extents.

The implementation details are specified in the BOOK OF IBUTTON STANDARDS.

W1 Master API

Zephyr’s 1-Wire Master API is used to interact with 1-Wire slave devices like temperature sensors and serial memories.

In Zephyr this API is split into the following layers.

The link layer handles basic communication functions such as bus reset, presence detect and bit transfer operations. It is the only hardware-dependent layer in Zephyr. This layer is supported by a driver using the Zephyr Universal Asynchronous Receiver-Transmitter (UART) interface, which should work on most Zephyr platforms. In the future, a GPIO/Timer based driver and hardware specific drivers might be added.
The 1-Wire network layer handles all means for slave identification and bus arbitration. This includes ROM commands like Match ROM, or Search ROM.
- All slave devices have a unique 64-bit identification number, which includes a 8-bit 1-Wire Family Code and a 8-bit CRC.
- In order to find slaves on the bus, the standard specifies an search algorithm which successively detects all slaves on the bus. This algorithm is described in detail by Maxim’s Applicationnote 187.
Transport layer and Presentation layer functions are not implemented in the generic 1-Wire driver and therefore must be handled in individual slave drivers.